This invention relates to a variable area exhaust nozzle for jet engine propelled aircraft and, more particularly, the invention is concerned with providing a variable area nozzle wherein the throat area configuration is controlled directly by high pressure duct nozzle air in accordance with engine requirements at various aircraft flight speeds.
It is well known that large nozzle variation is required in present generation high Mach jet engines for handling the expansion that occurs at supersonic velocities. Intensive studies have been made regarding the improvement of engine operating efficiency under disimilar flight conditions. For example, for subsonic flight speeds an efficient type of jet exhaust nozzle is one having a convergent shape and at near sonic and supersonic flight speeds, it is more desireable to employ a nozzle having a convergent nozzle followed by a divergent portion. For the most efficient operation it is desirable that the ratio of the throat area (area of minimum flow) to the exit area at the downstream end of the divergent portion be variable. The reason for this is that as flight speeds increase, the ratio of the pressure upstream of the throat to the pressure downstream thereof increases and it is necessary to increase the ratio of the exit area to the throat area in order to obtain efficient expansion.
Various convergent-divergent nozzles have been proposed having movable members which can vary the effective areas of the convergent and divergent portions. An accuation system for these types of convergent-divergent nozzle requires great flexibility which, in turn, necessitates the installation of heavy and complicated cam roller and/or gear type linkage arrangements. These presently available variable nozzle systems extract a high cost in weight and complexity as well as being more difficult to maintain and more subject to failure. Since the linkage arrangements are in a high temperature environment, the components such as air motors, cable drives, ball screws, etc. require cooling in order to survive.
Therefore, an ideal actuation system for controlling the throat area of a variable area nozzle would be one where the need for mechanical and/or hydraulic drives could be eliminated particularly in the high temperature environment of the exhaust nozzle. Also, the nozzle should be capable of being varied to provide configurations suitable for a wide range of operating conditions. The hereinafter described duct pressure actuated nozzle includes features which overcome the aforementioned disadvantages while at the same time provide a highly efficient system which is reliable and easily maintained.